The present invention relates to television receiver circuitry and more particularly to circuitry for reducing objectionable display effects due to the occurrence of noise in the video signal. A circuit is described for substituting delayed signal for noisy signal and simultaneously effectively reducing signal bandwidth when noise is present in the signal.
Defects or noise in television image information signals produce objectionable picture characteristics in the reproduced image in the form of bright or dark lines or spots or spots of varying color. In broadcast TV signals these defects arise from RF interference which impose noise impulses on the transmitted signals. A familiar manifestation of such noise are the bright flashes which occur on the TV display when an electric motor such as a hair dryer is operated in the vicinity of a TV receiver. With respect to video signal recovered from a recorded medium, e.g., playback of a VTR or a video disc, defects arise from loss of portions of the recorded signal due to defects in the record. These defects are referred to in the recording arts as dropouts and produce streaks in the displayed picture. Whether the defects arise from noise or dropouts they are susceptible of detection prior to display of the image so that corrective action may be taken to reduce objectionable manifestations.
Television image information is generally redundant line to line. It is therefore possible to substitute segments of signal from adjacent image lines in place of defective signal segments. Known defect compensators of this type, as shown in U.S. Pat. No. 2,996,576, store image information from a previous line and insert the stored previous line of information, or a portion thereof, into the video signal when a signal defect occurs. See also U.S. Pat. No. 4,122,489, "Signal Defect Compensator," Bolger et al.
It has been found to be advantageous to perform such signal substitution only if the signal is determined to be generally noisy. This may be accomplished by testing for the presence of noise during the vertical blanking interval and enabling the substitution circuitry for a preset number of successive fields or frames following the detection of noise in a vertical interval.
In order to enhance picture sharpness TV receivers frequently incorporate peaking circuitry to enhance higher frequency signal transactions. Unfortunately the peaking circuits also enhance noise components. Therefore it is desirable to defeat or reduce the effects of the peaking circuits in the presence of noise, see for example U.S. Pat. No. 4,081,836.